By bisecting, commit 415e72d03(md/raid5: Allow recovered part ofpartially recovered devices to be in-sync) was found as the cause offollow problem: * md1_raid5 or md1_raid6 process will hang(99% CPU usage) afterrepeatedly remove disk from then re-add disk to raid5 or raid6（thereis also a dd process write to the raid continuously).

Hardware platform is IOP 341 XScale processor(did not test on otherplatforms）. The problem can be reproduced with this script: